There are numerous devices for delivering medicament on the market and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. A very common design is a generally tubular compartment having a stopper in one end of the compartment and a delivery member attached to the opposite end of the compartment, such as, e.g., a needle, a nozzle or the like member capable of delivering medicament to a patient.
In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a plunger rod, which could be done manually by a finger, which is the case for simple handheld syringes, or by pressure means such as springs, which is common in automatic or semi-automatic injectors. In this context, the so called pen-injectors are becoming quite common, where the injection is performed by manually pushing at a distal end of the device. With this type of injector there has also been a development regarding delivering different dose quantities with the same device, i.e. to be able to set a certain prescribed dose before delivery.
A number of such devices have been developed, such as the device disclosed in EP-A-1 601 395. Here the device is arranged with a dose setting drum that can be rotated in relation to a housing and a drive sleeve that, upon manual operation by a user, drives a plunger rod to deliver a set dose of medicament. In order to provide the function of setting a dose with the dose setting drum and delivering a dose with the drive sleeve, there has to be some sort of connection/disconnection mechanism between them. Thereby a clutch or uni-directional connection mechanism has been developed for providing the desired function. This solution entails a number of components that are to interact with each other as well as a number of threaded engagement and connection mechanisms that require careful design in order for the manually applied force by a user not to be too large, or the device otherwise will not function properly. There is also a question whether the solution according to EP-A-1 601 395 can provide the possibility of resetting a set dose in a simple and efficient manner.
Another feature with the device of EP-A-1 601 395 is that the setting of a dose larger than the remaining quantity should be prevented in that when a nut reaches the end of a helical thread of the connection mechanism, the nut stops rotating of a dose dial sleeve and the drive sleeve will thus become locked together preventing rotation of the dose dial sleeve and setting of a larger dose. This direct action between threads is not so precise in that there is no distinct stop between the components. Rather, the components could be turned in relation to each other quite a turning distance before the friction becomes so high that it is difficult to turn them relative each other any longer. Thus, a user could then erroneously believe that he/she is receiving a larger dose than the actual dose received.
Further, the components, such as the dose setting drum and the drive sleeve as well as the plunger rod are elongated and positioned inside each other. In order to not risk a jamming between the components, a certain play is necessary. Then, such play and gaps between components increase the risk of lack of support and therefore rattling and other noises that may negatively affect a potential user.